Apple says you can't but others in another forum seem to contradict this. You are correct about Windows not being able to read a Mac iPod, although it may well be possible if you invest in additonal software that reads HFS on Windows.
Like iTunes, the Windows version is bundled with an application to use the iPod. The Windows iPod uses standard FAT32 filesystem on the HD, while the Mac version uses standard HFS+.
Apple seems to interpret "use an iPod with ..." to mean that it's supported with the bundled application.
Reading and writing to an iPod drive x-platform is another matter. Windows users can install 3rd-party SW that can read HFS+ and it seems Mac users can mount and access files on a Windows formatted iPod if they have the correct version of the OS. Assuming that goes well, you should be able to manually copy, write, and use the files. X-Play supports iPod on Windows if you have a Mac version of the iPod.
Some people report that OS9.2.2 and Jag can read them, but I can't confirm that myself. Since many digital cameras format their media cards as PC drives, it may well be possible to mount FAT32 disks (FAT16 is definitely supported in MacOS).
X-Play uses MediaFour's XDrive technology, and creates basically a folder on the iPod (when it is mounted and assigned a drive letter) called "Music" (or something like that) along with a fw othre folders fora few other things (I haven;t used the software since the second preview version, So I am not sure if it still works like that or with a software frontend.
The Windows iPod can be read by Jaguar. Plug it in and it works just like a Mac iPod would work, but with a generic icon on the desktop.
You can even use the iPod utility to restore a Windows iPod and it will still work with windows after.